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    Converting the battery voltage , help to a syrian xD

    ( I have already posted this thread in another website )
    hello my name is Manar 4th year (stopped studying) computer engineering bachelor , and I live still in Syria.
    As it can be called the silliest thing happening here , but it is annoying , that we don't get electricity most of the day .
    I am trying to build a battery for my internet router , I already have got the battery actually but I need to build the circuit so it gives what the router needs , the battery is 8.5 volts 2000 mA I got it from an old camera , and the router needs 12 volts and 1 A , the first thing is , how can I convert these 8,5 volts to 12 ? is there any way to do that ?
    thanks you very much
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    •   Alt16th January 2013, 20:14

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    Re: Converting the battery voltage , help to a syrian xD

    Perhaps, first check if 12V 1A is really needed. Most routers have circuitry to step down 12V to 5 Volt,3.3Volt and so forth already on board and input can vary from the 12V. So depending on the exact design of router circuitry the input may have a range to get 12W power needs, i.e. so with a 12V power supply 12V*1A = 12W but 8.5V*1.5 is circa 12W.



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    Re: Converting the battery voltage , help to a syrian xD

    Quote Originally Posted by cntube View Post
    Perhaps, first check if 12V 1A is really needed. Most routers have circuitry to step down 12V to 5 Volt,3.3Volt and so forth already on board and input can vary from the 12V. So depending on the exact design of router circuitry the input may have a range to get 12W power needs, i.e. so with a 12V power supply 12V*1A = 12W but 8.5V*1.5 is circa 12W.
    you are totally right ,
    how can I check if its needed ?
    and if its like that , you mean that if i put this 8.5 battery with an lm317 and set the current to 1.5 A and plug it to the router it will be on and ok ?
    thank u very much for the reply really
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    Re: Converting the battery voltage , help to a syrian xD

    A simple check is to use a lab power supply to set the input voltage to 8.5V and check router function. Going to a lower voltage will not damage anything but depending on the router circuitry may not function at the lower voltage.

    The LM317 is not needed because the router power supply will adjust automatically for input voltage variations, that is, increase current in take if the router has a switching converter, if a linear regulator is used, then current would remain about the same and actually the linear regulator will have to dissipate less power.


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    Re: Converting the battery voltage , help to a syrian xD

    Better open router and see inside whats on PCB. This can help you to understand what voltage router PCB need.

    Its big chance that is only 5V.


    Also You can post photos here.
    “Let the future tell the truth, and evaluate each one according to his work and accomplishments. The present is theirs; the future, for which I have really worked, is mine.” Nikola Tesla



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    Re: Converting the battery voltage , help to a syrian xD

    Quote Originally Posted by cntube View Post
    A simple check is to use a lab power supply to set the input voltage to 8.5V and check router function. Going to a lower voltage will not damage anything but depending on the router circuitry may not function at the lower voltage.

    The LM317 is not needed because the router power supply will adjust automatically for input voltage variations, that is, increase current in take if the router has a switching converter, if a linear regulator is used, then current would remain about the same and actually the linear regulator will have to dissipate less power.
    ummm these r useful information , I should have known that , but what would be the difference if i dont use a lab power supply and I hook the battery directly ?
    and u mean by that is that I am safe if I just hooked the V+ and the gnd of the battery to the router just like that without any driving circuit , it would works ?
    danke schon yet again
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    •   Alt17th January 2013, 22:55

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    Re: Converting the battery voltage , help to a syrian xD

    Battery dont have constant voltage level, voltage will drop on load and during discharging.

    This battery of 2Ah is not big. This is smaller in capacity from NiMh AA batteries (of course NiMh single cell is 1,2V bat in serie of 7-8 can make higher voltage). AA can have over 3Ah.
    “Let the future tell the truth, and evaluate each one according to his work and accomplishments. The present is theirs; the future, for which I have really worked, is mine.” Nikola Tesla



    •   Alt17th January 2013, 23:08

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    Re: Converting the battery voltage , help to a syrian xD

    Quote Originally Posted by tpetar View Post
    Battery dont have constant voltage level, voltage will drop on load and during discharging.

    This battery of 2Ah is not big. This is smaller in capacity from NiMh AA batteries (of course NiMh single cell is 1,2V bat in serie of 7-8 can make higher voltage). AA can have over 3Ah.
    actully my battery is an NiMh , I didn't understand what do you mean , but actully today i have hooked the battery and it didnt work well, but it was giving only 6 volts , but now iam going to fully recharge it and try again , but shouldn't I make a circuit that would keep the voltage constant ?
    thank uuuuu
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    Re: Converting the battery voltage , help to a syrian xD

    Better first check router PCB design in input power section, to se what voltages that device use. If you give 6V to router, there is a possibility to make some damage to IC parts. Usually used voltage regulators needs 2,5V-3V minimal Vi-Vo difference. You need to take into account that the battery full and empty have different voltages, that voltage will change during disharge process.
    “Let the future tell the truth, and evaluate each one according to his work and accomplishments. The present is theirs; the future, for which I have really worked, is mine.” Nikola Tesla


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    Re: Converting the battery voltage , help to a syrian xD

    The cell voltage does not vary a great deal, for example fully charged 4 cell NiMH measured around 6V. Used this output through a diode to drop 0.7V for 5V+-10% until battery flat at circa 5.2V. The power requirements for your router are small enough that a boost circuit, if needed could power the device, possibly letting one get every maH out of the cell before overdischarging. At least, it is not a requirement like a have 6V 5AH battery and want to make 1kW inverter:D.



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    Re: Converting the battery voltage , help to a syrian xD

    Quote Originally Posted by newbie noob View Post
    actully my battery is an NiMh , I didn't understand what do you mean , but actully today i have hooked the battery and it didnt work well, but it was giving only 6 volts , but now iam going to fully recharge it and try again , but shouldn't I make a circuit that would keep the voltage constant ?
    thank uuuuu
    If the battery voltage drops from 8.5V to 6V when loaded, then it is probably low on capacity and needs a recharge.

    The router certainly has internal voltage regulators, so your source voltage doesn't need to be well regulated. But it does need to be above some minimum voltage at all times. That minimum voltage is not certain, but it might be low enough that your battery can work. If not, you will need to make a boost converter of some type. What resources do you have for making circuitry?

    Good luck, please stay safe.


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    •   Alt18th January 2013, 17:35

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    Re: Converting the battery voltage , help to a syrian xD

    If you assume the 'router' requirements are correct and that it does require 12V at 1 A, I have no idea what kind of a router would use 12W so im a bit suspicious but assuming it does. then you need your circuit to be at least 70.5% efficient. Now assuming this is a rechargeable battery and that its only holding 80% of the capacity as it did when new out of the box, then you are looking at requiring a step up converter efficiency of over 88% (this is getting tougher now). The fact that when you plugged in the battery and it dropped to 6 volts means its underpowered(not able to sink the current demanded from the load), however if you are plugging it in directly the 'router' really requires 12V then it might be trying to sink more current then normal do to operating voltages being lower then required and circuitry not functioning correctly. As mtwieg mentioned it will have internal regulators requiring a min range, but 8/12 is only 66% of the value, i double any regulator works with that much undervoltage and maintains any type of efficiency ( remember you loose some power with regulators as well as the step up converter).



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    Re: Converting the battery voltage , help to a syrian xD

    Quote Originally Posted by mtwieg View Post
    If the battery voltage drops from 8.5V to 6V when loaded, then it is probably low on capacity and needs a recharge.

    The router certainly has internal voltage regulators, so your source voltage doesn't need to be well regulated. But it does need to be above some minimum voltage at all times. That minimum voltage is not certain, but it might be low enough that your battery can work. If not, you will need to make a boost converter of some type. What resources do you have for making circuitry?

    Good luck, please stay safe.
    ok this was helpful ! , that is what I was thinking of but couldn't get the name " boost circuit" , and for resources , most of them will be available , but I guess some would be not available of a company and it would be available by another one , I mean for example if an ic by National Instrument was not found , you can find the same ic but from another company , anyhow I will be able to get all of the parts if I was lucky ,
    I will try to look over the internet for a boost circuit and then come back here ,
    thank you very much
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    Re: Converting the battery voltage , help to a syrian xD

    Quote Originally Posted by mtwieg View Post
    If the battery voltage drops from 8.5V to 6V when loaded, then it is probably low on capacity and needs a recharge.

    The router certainly has internal voltage regulators, so your source voltage doesn't need to be well regulated. But it does need to be above some minimum voltage at all times. That minimum voltage is not certain, but it might be low enough that your battery can work. If not, you will need to make a boost converter of some type. What resources do you have for making circuitry?

    Good luck, please stay safe.
    mr mtwieg sorry if I was bothering you , but I found this circuit which steps up the voltage http://www.eleccircuit.com/dc-to-dc-...tor-by-lm2577/ but someone here has mentioned that using the lm317 with current regulating would disturb the circuit of the router and wont work probebly , does that so with lm2577 ? can you tell me if this circuit is suitable or not ? and I promise that this would be the last question
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    Re: Converting the battery voltage , help to a syrian xD

    You will have a loss of energy, and your batteries will not last long.
    “Let the future tell the truth, and evaluate each one according to his work and accomplishments. The present is theirs; the future, for which I have really worked, is mine.” Nikola Tesla



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    Re: Converting the battery voltage , help to a syrian xD

    This LM2577 circuit looks like it will meet requirements. However, the condition of the battery that you have on hand is the big question. Is the battery degraded or even rated for 2 Amp current draw? The conversion from 6V to 12V would require over 2A at 6V. Can the battery maintain 5-6V at over 2A draw? A load test would help determine this. That is just the POWER from battery requirements. The energy is stated to be 2000mAh so if the battery could give over 2A at 6V then the run time would be about 1 hour. There are a lot of details to consider. The efficiency of the converter would hinge on the inductor selection with due consideration for diode selection and output capacitor selection.



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